The present invention relates to an apparatus for preparing a working, processing or machining liquid of an electroerosion machine.
Electroerosion machines have a working container filled with a machining liquid in which a workpiece to be machined by electroerosion is immersed. In wire cutting or wire erosion machines, the machining liquid consists of deionized water, whereas in the case of countersinking machines it consists of hydrocarbons. As the erosive removal of particles from the workpiece takes place there is an eventual reduction in the cleanness of the machining liquid, so that its electrical conductivity changes. In order to maintain a desired quality of the erosion process, it is necessary to clean the machining liquid so as to maintain its electrical characteristics and cleanness within predetermined ranges.
Conventional filters are typically used for the preparation of the machining liquid, which have a comparatively large pore diameter. In the case of the large pore sizes of such conventional filters the filtering action is not adequate to maintain the quality of the machining liquid of an electroerosion machine within a desired quality range for a period of several days. A reduction in the pore diameter of conventional filters for increasing the filtering quality leads to the clogging of the filter walls.
It is generally known in the field of filter technology to use membrane filters, which have an extremely small pore cross-section compared with the pore sizes of conventional filters. However, membrane filters have been considered unsuitable for the coarse filtering of the concentrate in electroerosion, because as a result of the high solids content in the concentrate, there has been always fear for of a rapid clogging of the membrane filter.
Therefore membrane filters have only been used for extremely specialized purposes but have never been used for cleaning the concentrate in electroerosion machines. JP-OS 62-24917 discloses an apparatus for preparing a machining liquid of an electroerosion machine, in which a membrane filter is used. The known apparatus comprises a container for the machining liquid, which is subdivided by a cellophane membrane into two areas. The first area is connected by means of a pump, with which is connected in series a conventional filter, to the working area of the electroerosion machine. This working area can be, by means of a further pump, again discharged into the first area of the container. The second area of the container is connected by means of a yet another pump to an ion exchanger. The ion concentration in the second container area is well below the ion concentration in the first container area so that the ion exchanger can be operated with a low ion density favorable for its operating behavior. In the case of this known apparatus for preparing a machining liquid, a conventional filter is used for filtering the concentrate, whereas a membrane filter is used only for the adjustable reduction of the ion density for an ion exchanger circuit and not for cleaning or preparing the concentrate.